Authenticating cropped and resized images using distributed source coding and expectation maximization

Media authentication is important in content delivery via untrusted intermediaries, such as peer-to-peer (P2P) file sharing. Many differently encoded versions of a media file might exist. Our previous work applied distributed source coding not only to distinguish the legitimate diversity of encoded images from tampering but also localize the tampered regions in an image already deemed to be inauthentic. The authentication data supplied to the decoder consisted of a Slepian-Wolf encoded image projection. We extend our scheme to authenticate cropped and resized images using an Expectation Maximization algorithm. Experimental results demonstrate that the proposed algorithm can distinguish legitimate encodings of authentic cropped and resized images from illegitimately modified versions using authentication data of less than 250 bytes.